























•^KiiJ: ,$X :^3P: a^ ".^S^- .^^ -HBP- aV«^ »w«" -v 







F * ^ -J 


















J ^ 














^ ,.0 * 








'^ A* «#>• 




























Bureau of Mines Information Circular/1982 




Alarm System for Radiation 
Working Level, Fan Operation, 
and Air Door Position 



By J. C. Franklin, P. E. Barr, K. D. Weverstad, 
and C. T. Sheeran 




UNITED STATES DEPARTMENT OF THE INTERIOR 



ciiaJ- to&, bw-ivj"*)) 



Information Circular 8903 



Alarm System for Radiation 
Working Level, Fan Operation, 
and Air Door Position 



By J. C. Franklin, P. E. Barr, K. D. Weverstad, 
and C. T. Sheeran 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



This publication has been cataloged as follows: 




2<& 



? ql>1 



Alarm system for radiation working level, 


fan operation, 


and 


air 


door 


position. 












(Information circular 


/ United States 


Department of 


the 


Interior, 


Bureau of Mines ; 8903) 












Bibliography: p. 17. 


» 










Supt. of Docs, no.: I 


28.27:890 3. 










1. Mine ventilation- 


-Safety measures. 


2. Electronic al 


arm 


sys- 


terns. I. Franklin, J. C 


. (JohnC). II. Series: Informa 


cion 


circular 


(United States. Bureau o 


f Mines) ; 8903. 










TN295.U4 [TN301] 


622s [622\8] 


82-600 294 









CONTENTS 

Page 

Abs tract 1 

Introduction 2 

Alarm system 2 

Surface alarm receiver 2 

Underground alarm transmitter 3 

Monitors and detectors 5 

Working level monitor 5 

Microcomputer 7 

Installation suggestions 9 

Calibration procedure 10 

Maintenance 13 

Fan shutdown-air door position detectors 13 

System troubleshooting 14 

Receiver to transmitter 14 

Underground transmitter 14 

Transmitter to monitors or detectors 15 

Conclusions 17 

References 17 

ILLUSTRATIONS 

1 . Surface alarm receiver 3 

2 . Block diagram of alarm transmitter and receiver 4 

3 . Continuous working level area monitor 6 

4 . Data switchboard layout 7 

5. Data switchboard with example settings 8 

6 . SYM-1 microcomputer 9 

7. Calibration data sheet 11 

8. Block diagram for monitoring power loss to underground fans 13 








UNIT OF MEASURE ABBREVIATIONS 


USED 


IN 


THIS REPORT 


ac 


alternating current 


min 




minute 


amp 


ampere 


mm 




millimeter 


dc 


direct current 


sec 




second 


Hz 


hertz 


V 




volt 


hr 


hour 


WL 




working level 


1pm 


liter per minute 









ALARM SYSTEM FOR RADIATION WORKING LEVEL, FAN OPERATION, 

AND AIR DOOR POSITION 

By J. C. Franklin, 1 P. E. Barr, 2 K. D. Weverstad, 3 and C. T. Sheeran 4 



ABSTRACT 

A 32-channel continuous monitoring system has been developed to moni- 
tor radiation working level (WL), fan operation, and air door position. 
The system consists of a surface receiver unit and an underground trans- 
mitter that is connected to the various monitors. A continuous WL 
monitor used with the system can generate alarms at two different WL 
readings. One of these levels is variable from 0.00 to 0.99 WL and gen- 
erates an alarm on the surface receiver. The other level, fixed at 
1.0 WL, generates an underground alarm in the vicinity of the monitor. 

The detectors for fan operation and air door position work on the 
principle of a completed circuit to the underground transmitter (multi- 
plexer). When the circuit is broken, as is the case when a fan is off 
or an air door is open, an alarm is generated at the surface receiver. 
This alarm remains in effect until the circuit is completed, signifying 
the fan has been turned on or the air door has been closed. 

i Supervisory physical scientist. 
^Electronics technician. 
■^Engineering technician. 
^Mining engineer. 
All authors are with the Spokane Research Center, Bureau of Mines, Spokane, Wash. 



INTRODUCTION 



Exposure to decay products of radon 
presents a serious health hazard for 
underground personnel in uranium mines. 
The uranium mining industry presently 
uses grab sampling techniques, including 
the Kusnetz method and instant working 
level meters (IWLM's), for measuring per- 
sonnel exposure. Holub (_5)5 shows that 
these measurements are accurate when used 
properly; however, it has been shown by 
Franklin 02-3) that the concentration of 
radon and radon-daughters is constantly 
changing. Because of the continual vari- 
ation in the concentration, a system is 
needed that will alert the ventilation 
engineer before critical levels are 
reached. 



The Bureau of Mines has developed a 
system that interfaces to continuous WL 
monitors and will generate both surface 
and underground alarms. A surface alarm 
is sounded when the radiation level has 
exceeded a preset WL limit, variable 
from 0.00 to 0.99 WL. An underground 
alarm is also generated when 1.0 WL has 
been reached. 

Detectors have also been developed for 
the system that may be used to monitor 
the power to fans and the positions of 
air doors. These detectors will generate 
surface alarms when fans are off or when 
air doors are open. 



ALARM SYSTEM 



The basic system components include a 
surface alarm receiver, an underground 
alarm transmitter, and various detectors 
and monitors. The detectors and monitors 
will be discussed in a separate section. 
Current system hardware is capable of 
handling input from 32 underground sta- 
tions. Signals from these stations are 
fed through individual cables to the 
transmitter. The transmitter multiplexes 
this information to the surface receiver 
through a single cable. 

Surface Alarm Receiver 

The alarm status of each channel may be, 
monitored, both visually and audibly, by 
the surface alarm receiver shown in fig- 
ure 1. As each channel is sampled, its 
green indicator light will briefly extin- 
guish. If there is not an alarm present 
on that channel, no further change will 
be observed. However, if that channel is 
in an alarm state, its respective red in- 
dicator will light and an audio tone will 
generated unless audio alerts have been 
previously disabled for that channel. 
Separate red and green indicators are 
used so the operator can verify normal 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



alarm scanning in the absence of any 
alarms, and to provide a positive alert 
in the unlikely event of an indicator 
(LED) failure. This indicator operation 
is also backed up by an alarm summary 
signal light that will indicate an alarm 
on any channel. The red light and audio 
tone will only last for that channel's 
sample time slot (approximately one- 
eighth of a second) . Not only does this 
method of alarm display attract atten- 
tion, it quickly identifies the occur- 
rence of simultaneous alarms on several 
channels, owing to the length and pattern 
of alarm signals. 

Once the alarm is received, the oper- 
ator acknowledges each by switching the 
audio for each channel in alarm to an 
off-state. This gives the operator an 
indication of alarm status by light and 
switch position. Even if all power is 
lost to the receiver, the most recently 
updated status of each detector station 
is available by observing the audio 
switch for each channel. Once an alarm 
is received and acknowledged, the oper- 
ator can take corrective action by mine 
phone or by dispatching ventilation per- 
sonnel to the problem areas. 

All detectors and monitors are de- 
signed to provide a positive, fail-safe 




FIGURE 1. - Surface alarm receiver. 



indication of normal operation. A high 
WL reading, an electronic malfunction, a 
cut or shorted telemetry wire to the 
transmitter, or loss of power will cause 
an alarm on the surface alarm receiver. 
Should power be lost at the underground 
transmitter, all alarm sequencing would 
cease and the receiver would maintain an 
alarm indication on channel until power 
is restored. The receiver also has a 
clock-synchronous activity indicator and 
a test switch that will activate each 
channel's alarm indicators, both visual 
and audio. A remote audiovisual alarm 
station may be added to alert additional 
personnel to alarm conditions in the 
mine. 



Undergrou nd Alarm Transmitter 

Current system hardware allows up to 32 
individual stations to terminate at an 
underground central-alarm transmitter 
unit. From this location, a single te- 
lemetry cable is routed to the surface 
alarm receiver. Figure 2 shows the block 
diagram of both the transmitter and 
receiver. This cable is a dual shielded- 
pair conductor that carries status sig- 
nals from each station by means of time- 
division multiplexing techniques. The 
scan cycle time is 4 sec for all 32 
channels. 



Clock 
8 Hz 



Buffer 
amplifiers 

( 32 ) 



Optic 
isolators 

( 32 ) 



_ 1 



TT 



32-stage 
counter 



Sync 
generator 



V 



Digital 
multi- 
plexer 



Input enable 
switch ( 32 ) 



Remote detector 
inputs ( 32 max ) 



Output 
driver 



Shielded, 

twisted 

pair 



XXOOOOC 



Output 
driver 



Clock 
receiver 



Shielded, 

twisted 

pair 



DOCOOOOC 



m 



Data 
receiver 



7 



Alarm multiplexer 
block diagram 



Clock-sync 
indicator 



Buffer 
amplifier 



Sync 
detector 



Buffer 
amplifier 



Sonalert 



Underground 

alarm 
transmitter 



32-stage 
counter 



Digital 
demulti- 
plexer 



^r^ 



Alarm 

[*'\/ summary 
indicator 



Audio 
alert 
logic 

( 32 ) 



ni — 1/ 



Alarm- 
normal 
indicators 

( 32 ) 



Surface 

alarm 

receiver 



FIGURE 2. - Block diagram of alarm transmitter and receiver. 



Since monitors or detectors can be lo- 
cated in widely separated areas and 
served by different power stations, elec- 
trical isolation of the unit is of utmost 
importance. Therefore, each signal, as 
it arrives at the transmitter, is ter- 
minated at the input of an optical iso- 
lator circuit. As its name implies, the 
signal is passed from input to output in 
the form of light. In the optoisolator, 
a light -emit ting diode (LED) is optically 
coupled to a photodiode. When the LED is 
activated by the monitor or detector or 
other alarm interface (fan, pump, etc.), 
the photodiode conducts and passes 
this logic state onto other multiplexing 
circuitry. In this manner, all 32 inputs 
are isolated from the transmitter and 
from one another, preventing ground-loop 



voltages and unstable operation due to 
common mode currents. 

Each optical isolator output can be in- 
dividually enabled or disabled, thus 
allowing for maximum flexibility in 
grouping of signals for a system with 
less than 32 inputs. Each signal then 
passes through an amplifier with special 
noise-reduction characteristics to fur- 
ther refine logic states. These inverted 
signals then terminate in one of the 
four, eight-input multiplexer circuits. 

All that remains is to sample each sig- 
nal in a prescribed sequence and "tag" 
each one as a unique channel. An 8-Hz 
clock in the transmitter is used to se- 
quentially switch each of the 32 data 



inputs (0-31) onto a data output line to 
the surface alarm receiver. This same 
clock signal is sent to the receiver sta- 
tion to control the demultiplexing cir- 
cuitry. Each data input is identified by 
its respective time slot in the clock 
pulse-train. However, to attain accurate 
data transfer, the time-slot counters at 
each station (underground transmitter and 
surface receiver) must be in step. This 
is accomplished by making one timing slot 
unique in comparison to all others. 
Channel is twice the width of any other 
channel for detection at the receiver. 
This makes the system a synchronous data 
multiplexer. 



Both clock and data signals are routed 
simultaneously to the surface receiver. 
The clock signal drives a 32-stage coun- 
ter as in the transmitter. This clock 
signal is also monitored by a missing 
pulse detection circuit. When this cir- 
cuit "recognizes" channel 0's extra 
width, it resets the receiver's clock to 
zero and outputs that time slot. Each 
successive clock cycle will advance the 
receiver's time-slot counter, and the 
information on the data line from the 
transmitter will be synchronously decoded 
for each respective channel. 



MONITORS AND DETECTORS 



The alarm system was designed to oper- 
ate with continuous WL monitors and de- 
tectors for alarming when the circuit is 
broken. Other monitors with an analog 
output could be used to alarm when the 
output drops below a set voltage. 

The continuous WL monitors are designed 
so they can be used as a stand-alone mon- 
itor in small mines or as a part of the 
alarm system. As a stand-alone unit, 
the continuous WL monitor would just 
alarm for 1 WL or greater at the monitor 
itself. 

Working Level Monitor 

The detectors used in the working level 
monitors are Geiger-Mueller (GM) tubes. 
Nuclear disintegrations resulting in beta 
particle emissions will cause a detect- 
able pulse output from the GM tube. 
Droullard (1_) reports a complete descrip- 
tion for the operation of the GM tube 
detector. These detectors have been in 
use for several years in various mines 
with good results. The monitor described 
in this report, although similar to that 
described by Droullard, has been inter- 
faced to a microcomputer to convert raw 
count into WL's, display that value on 
the monitor itself, and energize the 
alarms when the set values are exceeded. 
Two alarms are possible from each monitor 



used with the system, one at the surface 
receiver, and the other at the monitor 
itself. The surface alarm limit is vari- 
able and its setting can be determined by 
company policy, while the underground 
alarm limit is fixed at 1.0 WL. The mon- 
itor is shown in figure 3. The housing 
is constructed of stainless steel with a 
rubber gasket around the lid to seal out 
moisture. The beta detector assembly is 
mounted on the lid for easy access in 
changing the 47-mm filter. 

Inside the housing are the power sup- 
plies for the GM tube and the microcom- 
puter, an airflow regulator, an airflow 
meter, a discriminator pulse-shaping 
card, and a data switchboard. This board 
is used for setting detector background, 
sample time, calibration factor, and var- 
iable alarm point setting values for re- 
tention during a power loss. A SYM-1 6 
microcomputer completes the major portion 
of the monitor components. There is a 
switch for shutting off the pump when 
background measurements are being made 
and a 2-amp fuse for the complete system. 

Figure 4 shows the layout of the data 
switchboard. The top row (six switches) 

"Reference to specific equipment is 
made for identification only and does not 
imply endorsement by the Bureau of Mines. 






■'■■- 



FIGURE 3, = Continuous working level area monitor, 



Telemetry 



Surface—, 



Alarms 
indicators 
( LED's ) 

Surface 

output 

interface 

Underground 

output 

interface 



r- Under 



w w w 



(-Switch settings for 
microcomputer 



ooo 




I0J I0J I0J I0J IM^ 

Background 

BB BB Mfr~li Reiay 

Calibration factor > 

BE 

Time 






S u rf ac e' J 

alarm 



IC chips 



][ 



Connectors 



Exponent 



Data switches 

FIGURE 4. - Data switchboard layout. 



is used for setting the gamma background. 
Because background is dependent on 
location, this setting must be adjusted 
each time the monitor is installed. 
The procedure for taking back- 
grounds will be described in a later 
section of this paper. The second 
row (six switches) is used for 
setting the monitor calibration factor 
(C.F.). 



This calibration factor takes into 
account the counting characteristics of 
the monitor, and is also influenced by 
the airflow rate (usually 1.0 1pm). If 
the C.F. has previously been determined 
for a different airflow rate than what is 
desired, the new C.F. can be calculated 
by simply dividing the old factor by the 
new airflow rate. This is represented by 
the following equation: 



C.F. for old airflow rate 
new airflow rate 



= C.F. (new). 



(1) 



The third row of switches is used to 
set time interval (left two switches) and 
surface alarm limit (right two switches). 
The time interval can be set from 1 to 
99 min, while the surface alarm can be 
set from 0.01 to 0.99 WL. 

Figure 5 shows how the switches would 
be set if the following parameters were 
used: 

Background 9387 

Calibration factor 6.47 x 10 _£ + 



Time 5 min 

Surface alarm 0.50 

Microcomputer 

The microcomputer (fig. 6) is the SYM-1 
single-board computer. It is an 8-bit, 
6502 microprocessor-based system with 
input-output interfaces, random access 
memory (RAM), read-only memory/erasable 
programable read-only memory (ROM/EPROM) , 
clock generator, RS-232C interface, oper- 
ator keyboard, and a six-digit output 



Telemetry 



Surface—, 
Alarms 
indicators 
( LED's ) 

Surface 

output 

interface 



Underground 

output 

interface 




Under 



i-Switch settings for 
microcomputer 



000 @ !•£ 

Background 
Calibration factor 



iej[*5| 
Time 




Surface* J 

alarm 



IC chips 



Connectors 



Exponent 



Data switches 

FIGURE 5. - Data switchboard with example settings. 



display. Software and descriptions of 
the microprocessor are described by 
Franklin (4_) and Shaw ( 6_) . 

Upon applying power to the monitor, a 
power-on reset signal is generated that 
resets all input-output interfaces, in- 
cluding timers and counters, in the 
microprocessor. The monitor operating 
parameters are read from the data 
switches and stored, and all alarm flags 
are cleared. There are five diagnostics 
that should be run to ensure proper 
operation of the microcomputer. When 
the reset key is pressed, the operator 
has 10 sec to select the diagnostic to 
be performed. The diagnostics are as 
follows: 

Reset A: Sequences the alarm condi- 
tions in 10-sec intervals. If the sur- 
face alarm switches are set above 0.30 
WL, both the yellow (surface) and 
red (underground) LED lights will come 
on together. If set below this level, 
each will come on separately — surface 
followed by underground. These alarms 



will clear in reverse order. The display 
will spell out the alarm states as they 
cycle. 

Reset B: Displays background measure- 
ments for the GM tube. 

Reset C: Performs diagnostics for math 
routines by inserting preset count, back- 
ground, calibration factor, and time into 
calculations. A display of 77.77 WL in- 
dicates the math routines are operating 
normally. 

Reset D: Reads the data switches and 
displays each value for verification. 

Reset E: Starts timer that will read 
up to 99 min and 59 sec. 

Upon completion of checks, push reset; 
after 10 sec, with no further keyboard 
entry, the main program locks in. The 
mine air monitoring cycle for WL then 
begins and repeats according to the sam- 
ple time selected. 




FIGURE 6. - SYM-1 microcomputer. 



Installation Suggestions 

Site selection for each monitor should 
be carefully made. The monitor should be 
placed in a working area such that air 
sampling will be representative of the 
entire work area. To determine a good 
site, WL samples should be taken in sev- 
eral locations in the stope or heading to 
determine an average concentration. Pro- 
cedures for taking these samples will be 
addressed in the section discussing 
equipment calibration. 

Once the general area has been located, 
several other factors must be considered. 
First, the monitor should be installed so 
that it will not be damaged by personnel, 



vehicles, slushing cables, or other 
equipment. The ideal location would be 
to suspend the monitor midpoint in the 
drift facing into air and away from in- 
tersections. If it is not possible to 
suspend the monitor in the center of the 
drift, it can be installed on the rib. 

Extreme care should be taken to ensure 
the monitor is not in a direct line of 
blasting or placed under loose rocks. 
Also, it is important to ensure that the 
location is safe for personnel to stand 
in while checking the equipment. 

This monitor requires 120-vac, 2.0- 
amp electrical power. Power is connected 
to the monitor through the three-pin 



10 



connector located on the left side of the 
housing. Power should only be applied 
when the monitor is ready for calibration 
and after careful inspection for loose 
integrated-circuit chips, connectors, 
electrical wires, or bolts. 

The five-pin connector, located on the 
bottom-right side of the housing, sends 
the alarm signal to the surface and un- 
derground alarm indicators. The con- 
nector is wired so that pins A and B are 
the signal wires going to the multiplexer 
transmitter. Pins C and D are used to 
connect the relay switch in the under- 
ground alarm detector to a local alarm. 
Pin E is for grounding purposes. 

Calibration Procedure 

Depending upon the number of monitors 
to be used, there are two ways to cali- 
brate them. One way, using only a few 
monitors, would be the individual cali- 
bration of each monitor in its final lo- 
cation. With a larger number of moni- 
tors, group calibration in an undisturbed 
drift with a relatively constant WL would 
be more time-effective. The second meth- 
od is described below. In this case, 
place the monitors facing the airstream 
and calibrate them all at the same time. 

Either the Kusnetz method or an instant 
working level meter (IWLM) may be used to 
determine WL for monitor calibration 
(step 12). Normally, the WL monitor 
would be calibrated with whatever method 
the mine currently uses. 

To determine the calibration factor for 
the continuous WL monitor, a step-by-step 
procedure is as follows: 

1. Hang all WL monitors at the same 
level in an undisturbed drift with a 
radon-daughter concentration of approxi- 
mately 0.3 to 0.5 WL. 

2. Make sure that all pumps are shut 
off before connecting power. 

3. Place a new 47-mm filter in each WL 
monitor. 



4. Turn power on. 

5. Set the sample time into the data 
switches (two lower left-hand switches). 
Normally a 5-min count is used. 



6. Push "Reset" "B" on the microcom- 
puter keyboard. Do this to each monitor 
at 10-sec intervals. This will start the 
WL monitors taking background data. Fig- 
ure 7 is an example to use for recording 
data during calibration. These data 
should be kept for future reference. 

7. Take at least five 5-min counts. 
Record the counts, then total and average 
for each WL monitor. This is the WL mon- 
itor background. 

8. Take the average backgrounds just 
calculated and set them on the data 
switches in each WL monitor. (The back- 
ground data switches are the top row of 
switches. ) 

9. Turn on the pump. 

10. Hook a section of tygon tubing 
between the exhaust of the WL monitor and 
a volumetric-flow measuring instrument. 
Time the flow with a stopwatch for 1 min 
to determine actual flow rate. If flow 
is not 1.0 1pm, then adjust the flow and 
take several more readings to be sure it 
is accurate and holding steady. Do this 
to each WL monitor to be calibrated. 

11. Actual calibration may now be 
started. Place a new filter in each WL 
monitor and let run for at least 3 hr be- 
fore taking the first count. 



12. Push "Reset" "B" on the microcom- 
puter keyboard. Do this to each monitor 
at 10-sec intervals. This will start the 
WL monitors taking data. At the same 
time, mine personnel should start taking 
a sample with their instrument and re- 
cording the WL that they obtain. Cor- 
responding samples must be taken at the 
same time with both the mine instrument 
and the monitors. 



11 



DATE 

LOCATION 
OPERATOR 



DETECTOR NO 



FLOW 



BACKGROUND 



(1) Count (2) Count-BG 



(3) Count-BG 
Time 



(4) WL 



Source 



A V 



FIGURE 7. - Calibration data sheeto 



12 



13. Take at least five 5-min counts on 
each monitor. Record the counts, then 
total and average for each WL monitor. 
This value is the Raw Count. 

14. The WL measurements taken by mine 
personnel during the same time-intervals 
should now be totaled and averaged. 

15. The calibration factor for each WL 
monitor can now be calculated by using 
the averaged data in the following 
equation: 



(WL) (sample time) 
Raw count - background 



= C.F. 



(2) 



The WL above is that obtained by Kusnetz 
or IWLM methods. The value obtained must 
be expressed in scientific notation be- 
fore being set in the data switches. An 
example of this calculation is presented 
at the end of these instructions. 

16. Take the calibration factor and 
set it in the second row of data switches 
in the WL monitor. NOTE: The second 
from the right data switch designates 
whether your power 10 number is a posi- 
tive or negative number. The switch set 
in the "0" position indicates a positive 
power, while "1" indicates a negative 
power. The far-right switch indicates 
the power of 10. The data switchboard 
has a decimal hard-wired in between the 
first and second switch from the left. 

17. Obtain source counts for each mon- 
itor by placing a known (cesium-137) 
source in the filter mount and recording 
at least five samples. 

18. Take the WL monitors from the 
calibration area and hook them up in 
their respective locations within the 
mine. 

19. Discuss with mine personnel as to 
what WL limit is desired for the variable 



setpoint surface alarm. Approximately 
0.7 WL is recommended, but it may be 
anything under 1.0 WL. Set this figure 
into the two lower right-hand data 
switches. 

20. Replace the filter in the WL moni- 
tor. Before taking a new background 
count, make sure that at least 3 hr have 
passed since the pump was shut off during 
calibration. Push "Reset" "B" on the 
microcomputer keyboard. Take at least 
five 5-min counts. Record the counts, 
then total and average them for the new 
background. Set this new background into 
the WL monitor through the use of the 
data switches. 

21. Set the airflow to the desired 
level using the volumetric flowmeter. If 
any flow other than 1.0 1pm is used, the 
calibration factor has to be corrected 
for the new flow rate. Make a mark with 
a grease pencil on the flowmeter, indi- 
cating the level that the flow ball is to 
reach. (This should be checked at least 
weekly during the test to ensure proper 
air intake. ) 

22. Run the diagnostic subroutine test 
programs that have previously been 
discussed. 

23. Push "Reset" to monitor the work- 
ing level in this particular area. 

As an example for calculating calibra- 
tion factor, the following data are used: 



Raw Count: 


8593 


Backgi 


•ound: 


154 


Time: 




5.0 min 


Flow: 




1.0 1pm 


WL: 




0.43 



13 



Raw count - background _ 
Time 



(3) 



8595 - 154 
5.0 



= 1687.8. 



0.43 
1687.8 



= 0.0002547695 = 2.55 x 10 -lf . (4) 



Equation 3 will convert net count into 
counts per minute, while equation 4 will 
convert counts per minute into WL per 
count at the 1.0-lpm flow rate. This is 
the calibration factor. If the flow rate 
has been changed after the monitor has 
been relocated, obtain the new C.F. by 
dividing the original C.F. by the new 
flow rate (eq. 1). Set this new C.F. 
into the data switches. 

Maintenance 

The 47-mm filter should be changed at 
least once a week and more often if the 
filter becomes plugged with diesel smoke 
and dust, or saturated with moisture from 
humidity. When replacing this filter, 
extreme care should be used to prevent 
damage to the backup screen (do not use a 
knife or screwdriver blade to remove the 
filter). The flowmeter should be read at 
the same time to ensure that the desired 
air volume is being taken. If not, ad- 
just the flow with the flow regulator and 
recheck about 1 hr later. 

Once a month, the cesium-137 source 
should be counted on each WL monitor with 
the pump off and a clean filter placed in 
the holder. After counting the source, 
recheck the background with the pump off 
and the source removed. The airflow 
should also be recalibrated monthly to 
ensure proper flow. 

The diagnostic routines should also be 
checked monthly to ensure proper opera- 
tion of the microcomputer and to verify 
that the data switches have not been 
changed. Visual inspection of all signal 
cables should be made when walking 
through the drifts. 



Fan Shutdown-Air Door Position Detectors 

Although the alarm system was primarily 
designed to alert for high radiation lev- 
els, it can also be used with special 
detectors to monitor fan shutdowns and 
air door positions. These factors are 
important in controlling the underground 
radiation hazard. 

If the underground fans are shut off, 
the fresh air to the face will stop or be 
greatly reduced, eventually causing a WL 
alarm condition. Therefore, a unit was 
designed to detect loss of power to the 
fan (fig. 8). 

When ac power is lost or shut off to 
the fan, an alarm condition will result 
on the receiver located on the surface. 
This alarm system works on a closed- 
circuit principle where a completed cir- 
cuit is necessary for a no-alarm condi- 
tion. An alarm will occur if any part of 
the circuit fails that is needed to carry 
the signal to the underground alarm 
transmitter. A red-light alarm on the 



Surface 
alarm monitor 



Single computer cable 



Underground 
alarm transmitter 



5-to 12-vdc signal 



Fan 
shutdown box 



120 vac 



480-to 120-vac 
t r an sf or mer 



I 



Fan motor 



480 vac 



Power switch 



480 vac 

■* 



mine 
power 



FIGURE 8. - Block diagram for monitoring power 
loss to underground fans. 



14 



surface receiver will be displayed show- 
ing the channel number corresponding to 
the fan location. 

In figure 8, it can be seen that the 
circuit to the detector obtains power 
from the same 480 vac that supplies the 
fan motor. By tapping off at a point 
between the fan motor and power switch, 
both ac power monitoring and switch mon- 
itoring are possible. In the event of an 
off-switch, power failure in the mine, 
electronic problem, or a cut cable, an 
alarm will result. 

Using the same switched 480 vac to the 
fan motor, a stepdown transformer brings 



the voltage down to a usable 120 vac for 
the electronics in the fan shutdown de- 
tector. A power supply within the detec- 
tor transforms the 120 vac into 9 vdc 
needed for the electronic circuit. This 
dependent electronic circuit then drives 
the signal (necessary for a no-alarm 
state) to one channel in the transmitter. 
The fan shutdown detector can easily be 
modified to monitor air door position by 
inserting a microswitch into the same 
electronic circuit. In figure 8, a mi- 
croswitch is placed on or at the door so 
that the switch will break the circuit 
when the door is opened. This broken 
circuit will result in an alarm being 
sent to the surface receiver. 



SYSTEM TROUBLESHOOTING 



System troubleshooting can be simpli- 
fied by using the LED indicators present 
on each device to diagnose possible prob- 
lems. There are two vital links in the 
system that will be treated separately in 
the troubleshooting. These are the 
receiver-to-transmitter connection and 
the connection between the transmitter 
and the monitors or detectors. 

Receiver to Transmitter 

All data concerning the underground 
stations are communicated through a 
single cable from the transmitter. Be- 
cause of this, this connection is vital 
in the fail-safe, signal-dependent alarm 
system. 

The transmitter generates a clock sig- 
nal with which the surface receiver has 
to synchronize before sequencing of the 
channels will begin. A lockup situation 
on channel of the receiver may be 
caused by the following: 

1. Transmitter turned off or power 
disconnected. 



2. Cut cable, power loss, 
splicing connection. 



or bad 



An alarm check switch on the receiver 
will check the sequencing of the LED's 



and may also be used to check for any 
that have burned out. A backup LED 
labeled "ALARM" (red color) allows 
any burned-out LED to be monitored in 
the sequencing channels. Also, a clock- 
synchronized LED flashes to indicate the 
incoming clock signal from the trans- 
mitter. Through the use of these 
indicators, various problems can be 
determined from the surface if the system 
fails or if a true alarm condition is 
present. 

Underground Transmitter 

The transmitter's front panel contains 
the following items : 

1. Green LED (monitors 5-v power 
supply needed for electronics). 

2. Yellow LED (flashes to indicate 
unit is sending out a clock signal to the 
surface receiver) . 

3. Red LED (comes on when activated 
channels are in alarm status — may be pro- 
duced by unhooked connectors, broken sig- 
nal cables, power loss, or an alarm sig- 
nal from the monitors or detectors). 

4. Red neon lamp (indicates 120 vac 
power is on) . 



15 



Green LED 



ON 

OFF 

Urr » • t • » • i * * i • * • o • 



Red LED 



Flashing 
Flashing 
OFF 



Yellow LED 



Flashing 

Flashing 

OFF 



Red neon 



ON 
ON 
ON 



Explanation 



Normal. 

Green LED burned out, 
C 1 ) 



1 Check the fuse and connections to and from the 5-v power supply, also 
check the 5 vdc out of the power supply to the electronics. If all connec- 
tions are secure and there is no signal from the power supply, it may be 
defective and need replacement. 



5. Keyed switch (on-off for 120 vac to 
transmitter) . 

6. Three-pin connector (120-vac power 
input connection) . 

7. Five-pin connector (signal cable 
connection to surface receiver) . 

8. Elapsed time counter (displays 
hours of use). 

The key troubleshooting areas to look 
for in the underground transmitter are 
the LED's and the neon lamp. Conditions 
that may occur are listed in the above 
tabulation. 

Transmitter to Monitors or Detectors 

Whenever a monitor or detector is con- 
nected to the underground alarm trans- 
mitter, certain procedures will enhance 
installation and minimize problems. 
Cable should be installed in locations 
where minimal damage will occur, such as 
on the back or behind vent bags. They 
should not be attached to power, com- 
pressed air, or water lines. Butt splic- 
ing should be correctly performed and 
used with water-protective tape. Keep 
detectors and cables out of water and 
secured effectively to prevent them from 
falling. 

Once the signal cable is connected to 
the surface alarm receiver and the under- 
ground alarm transmitter, a signal cable 
from a monitor or detector can be 
attached to the appropriate channel con- 
nection on the back of the underground 
alarm transmitter. The back panel of the 



unit has 32 connectors corresponding to 
channels labeled from to 31. For exam- 
ple, if channel was connected to a sig- 
nal cable, the other end would be con- 
nected to a monitor or detector in a 
selected location in the mine. After a 
monitor has been installed with ac power 
on, signal cable connection can then be 
made. 

The working level monitor contains the 
following LED's which can be used to di- 
agnose problems : 

1. Red (on flowmeter) — flashes as 
pulses are processed from the GM tube 
through the amplifier and discriminating 
pulse-shaping card. 

2. Green (on data switchboard) — when 
on, indicates communication with trans- 
mitter via the signal cable (telemetry). 

3. Yellow (on data switchboard) — when 
on, indicates an underground alarm condi- 
tion (^_1.0 WL). 

4. Red (on data switchboard) — when on, 
indicates the variable setpoint alarm 
limit has been exceeded and that an alarm 
is being sent to the surface through the 
underground transmitter. 

Once the connection to the working 
level monitor has been made and the 
telemetry light shows a completed con- 
nection to the underground alarm trans- 
mitter, the following procedures should 
be performed: 

1. Check filter on GM tube for clean- 
liness and correct installation. 



16 



2. Check various cable connections in- 
side the monitor box for secure contact. 

3. Check integrated circuits and data 
switch chips for contact in appropriate 
socket. 

4. Check red (LED) light on flowmeter 
for a flashing, incoming count from the 
GM tube. 

Conditions that may occur with the 
monitor LED's are listed in the tabula- 
tion below. 

As a final check, perform the micro- 
computer diagnostics explained earlier in 
this report. When a reset "A" is acti- 
vated on the computer, the alarm sequence 



subroutine will 
no-alarm state, 
from the comput 
three LED's on 
green LED will 
three periods 
display on the 



cycle through the alarm, 
This alarm signal output 
er can be monitored by the 
the data switchboard. The 
be on during the first 
of the cycle in which the 
computer will show "ALA." 



At the beginning of the fourth alarm 
cycle, the display will change to "ALA- 
US" to show an underground and surface 
alarm status. The computer at that in- 
stant puts the monitor in alarm status by 
turning off the green telemetry LED and 
turning on the yellow and red LED's, thus 
indicating that the underground alarm 
light is on and that the surface alarm is 
being sent from the monitor to the under- 
ground alarm transmitter. The alarm for 



Red (flowmeter) 


Green on data 
switchboard 


Yellow 


Red 


Explanation 




ON 


OFF 


OFF 


Normal operation, no WL alarms. 




OFF 


OFF 


OFF 


C 1 ) 




OFF 


OFF 


ON 


Normal operation, variable setpoint 
alarm limit exceeded and surface alarm 
being generated. 




OFF 


ON 


ON 


Normal operation, both alarm limits 
have been exceeded and both underground 
and surface alarms are being generated. 




- 


- 


- 


( 2 ) 



"^May be due to several problems including cut or unconnected cable, monitor power 
off, or the optoisolator for that channel in the transmitter is defective. Find out 
if the monitor is defective by replacing it with another unit. If the green light is 
still not on, the first monitor is probably all right. Check connections and cables, 
and also verify that there is power to the transmitter. If these check out, the op- 
toisolator for that channel in the transmitter is probably at fault and should be 
replaced. 

2 GM tube, amplifier circuit, GM power supply, discriminating pulse-shaping card, or 
LED could be defective. Use the following procedure: 



1. Perform a "Reset' 
mal count is displayed 
out. 



"B" on the microcomputer to check for pulse input. If a nor- 
at the end of the count period, the LED is probably burned 



2. In the event there is no pulse input to the microcomputer, use a voltmeter to 
check the output of the power supply (1,000 vdc) and check connections or replace 
power supply if defective. 

3. Use an oscilloscope to verify pulse output from the GM tube and amplifier 
circuit — replace parts as necessary. 

4. If all else checks out, the problem lies in the discriminating pulse-shaping 
card. Replace or repair as needed. 



17 



"US" will cycle four times and then re- 
turn to a no-alarm state. This will con- 
tinue until "reset" is pressed. 

When the troubleshooting techniques 
unique to the working level monitor have 
been satisfactorily performed (power 
cables, alarms, telemetry checks, and a 
flashing red LED on the flowmeter), push 
"reset" on the computer and close the 
lid. Wait to ensure that the main pro- 
gram has taken over and is displaying 
working level readings. 

The fan operation and air door position 
detectors both contain a single, green 



LED that can be used for troubleshooting. 
When the detectors are properly in- 
stalled, the green LED should light when 
the signal cable from the underground 
transmitter is hooked up (assuming the 
fan is on or air door is closed). If it 
does not light, the LED may be burned out 
or power may be off to the detector. 
Check this by shorting across the output 
connector to light the LED. If this is 
normal, then the problem is in the con- 
nection to the underground transmit- 
ter and may be due to a cable fault 
or a defective optoisolator in the 
transmitter. 



CONCLUSIONS 



Through the use of this alarm system, 
the ventilation engineer will be able to 
detect when underground fans are oper- 
ating, air doors are open, the WL 
has reached the company's shutdown lev- 
el, and when 1 WL has been reached. 
By early detection of fan shutdown or 
reaching the company's desired maximum 
limit, the miners can be withdrawn 
from areas while corrective action 



is taken to prevent excessive radiation 
exposures. 

The WL monitors can be used as a stand- 
alone unit in small mining operations 
without the use of the multiplexer trans- 
mitter and receiver. This would still 
alert the miners when excessive radiation 
levels are being approached so that cor- 
rective action can be taken. 



REFERENCES 



1. Droullard, R. F. , and R. F. Holub. 
Continuous Working-Level Measurements Us- 
ing Alpha or Beta Detectors. BuMines RI 
8236, 1977, 14 pp. 

2. Franklin, J. C. , T. 0. Meyer, R. W. 
McKibbin, and J. C. Kerkering. A Contin- 
uous Radon Survey in an Active Uranium 
Mine. Min. Eng. , v. 30, No. 6, June 

1978, pp. 647-649. 

3. Franklin, J. C, C. S. Musulin, and 
R. C. Bates. Monitoring and Control of 
Radon Hazards. Proc. 2d Internat. Mine 
Ventilation Cong., Reno, Nev. , Nov. 4-8, 

1979, Society of Mining Engineers of 
America Institute of Mining, Metallurgi- 
cal, and Petroleum Engineers, Inc., New 
York, 1980, pp. 405-411. 



4. Franklin, J. C. , and D. M. Shaw. 
Airborne Radiation Monitoring System. 
Proc. Radiation Hazards in Mining: Con- 
trol, Measurement, and Medical Aspects, 
Golden, Colo., Oct. 4-9, 1981, Society 
of Mining Engineers of America Institute 
of Mining, Metallurgical, and Petro- 
leum Engineers, Inc., New York, 1981, 
pp. 980-983. 

5. Holub, R. F. Evaluation and Modi- 
fication of Working-Level Measurement 
Methods. Health Phys., v. 39, September 
1980, pp. 425-447. 

6. Shaw, D. M. , and J. C. Franklin. 
Continuous Radiation Monitoring/Alarm 
System. Eng. and Min. J., v. 183, No. 5, 
May 1982, pp. 84-90. 



INT.-BU.OF MINES, PGH.P A, 26466 










'75 83 



<* '•".".* .0"** *o 7Z % \& 







«5°* 






** A* • 



V ^ 






V ^ 






iir\ c° •:&& °* AtfJfcr % * -Sate * /\c^\ e°*.jSfc>o /\< 



•> v*^V v^>" V^V V^V .%^ff?v V 



^\ 







;- '++J s&NS: «bf :£mx~ '^0* 







"bv* 






►* 









*% 






V 



f^^l 



i^^i 



v ^-. V" ° t 



o V 



;. *^ o T 

















/ v^ f >* °°*^V V*^V %'^V 






" * « • 



* ^ 



45 °«* 



.- ^^ 



/^ 



^ 



«*°* 



















->. 



apr 83 ^ * \ i^ffiJ' * v^^y * ^v^^V^ " v^^" V ' 

N.MANCHESTER, «<T • « « •# *^ 0^ .•M'*^ O^ . « * », ^> \> .•"'^ ^ 0^ .«•«>, 



